Cathode sleeve



Dec. 16, 1941-. N. H. GREEN 1 2,266,622

CATHODE SLEEVE Filed July 51, 1940 MENTOR- NORVAL H. GREEN AITORNEY Patented Dec. 16, 1941 CATHODE SLEEVE Norval H. Green, Wood-Ridge, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 31, 1940, Serial No. 348,771

3 Claims.

My invention relates to cathodes for electron discharge devices, particularly to indirectly heated cathode sleeves for such devices.

Cathode sleeves held at both ends in holes in insulating spacers must fit snugly in the holes to prevent lateral movement of the sleeve, yet must be free enough in the holes to permit longitudinal expansion when heated. A sleeve in oversized holes may vibrate and cause the radio tube to be microphonic whereas a sleeve forced into undersized holes may buckle and bow when heated. Variations in sizes of sleeves and spacer holes encountered in the usual manufacturing technique cause considerable difficulty in the asseimbly of radio tubes with properly fitted cath- 0 es.

The object of my invention is a cathode sleeve that may be held against lateral movement in insulating spacers yet without binding and which is easy to make and assemble with the spacers.

The characteristic features of my invention are defined in the appended claims and the preferred embodiment thereof is described in the following specification and shown in the accompanying drawing in which Figure 1 is an elevational view, partly in section of my improved sleeve, Figure 2 is an end view of my sleeve in place in the hole of an insulating spacer, and Figure 3 is an elevational view, partly in section, of an electron discharge device with my improved cathode.

My improved cathode'sleeve or sheet metal cylinder I, internally heated with an insulated heating element and exteriorly coated with active metal oxides, is supported at its ends in platelike insulated spacers 2, usually of thin friable material, such as mica, concentric with grid 3 and anode 4. The ends of my improved cathode are so shaped that the sleeve is snugly held in the spacers so that the sleeve cannot vibrate to change the cathode-to-grid spacing or cause troublesome microphonic vibrations in space current. The sleeve slips easily at either end into the hole in the spacer and is free to expand longitudinally when heated.

My improved sleeve, shown in greater detail in Figure 1, may be of the drawn seamless type or may be of the type that is rolled from flat stock and seamed along one side. Preferably a connecting tab 5 is formed at one end of the sleeve. Narrow elongated ridges 6 are formed in the Wall of the sleeve Where the spacers engage the sleeve. Ridges 6 may be conveniently pressed or embossed in the flat sheet metal stock and then rolled into the cylinder and closed by a conventional lock seam. Alternatively, short lengths of Wire may be spot welded to the side of the sleeve. A circumferential embossed bead 1 may conveniently be made at one end of the sleeve to bear against one spacer and longitudinally locate the sleeve in its mount.

The hole in the spacer for receiving the sleeve is, as shown in Figure 2, slightly larger in diameter than the sleeve, yet is less than the diametrical distance through the sleeve and the ridge 5. As the end of the sleeve is passed into the spacer hole the rounded and tapered end of the ridge 6 cuts into the edge of the hole forcing the sleeve against the opposite side of the hole. The normal diameter of sleeve, size of the hole, and height of ridge are preferably chosen so that the ridge is embedded about one-half its depth into the edge of the hole. In addition to providing an optimum fit between all cathodes and spacers having normal dimensional variations my novel cathode reduces the area of contact between the sleeve and its supports and minimizes end cooling. The wedging action of the ridge may in some cases slightly distort the sleeve and may press the sleeve into contact with as much as one-half of the periphery of the hole. .,Go0d results have been obtained with cathode sleeves about one inch long and .045 to .046 inch in diameter when assembled with spacers having cathode sleeve holes .046 to .047 inch in diameter and with ridges, substantially as shown, about .003 inch in height above the surface of the sleeve.

My novel cathode sleeve is held against lateral movement in insulating spacers, yet is not bound so that it will bow or buckle when heated and is easy to make and assemble with the spacers.

I claim:

1. An electron discharge device comprising a thin walled tubular cathode, an insulating spacer with a hole to receive one end of said cathode, said hole being slightly larger in diameter than said sleeve, means to prevent lateral movement of said sleeve in said hole comprising a longitudinal ridge on said sleeve where the sleeve passes through said hole, said ridge being relatively sharp and embedded in the edge of said hole.

2. An electron discharge device comprising an envelope, an electrode assembly in said envelope including an anode, a grid, and a cathode sleeve, a mica spacer attached to the electrodes at one end of the assembly, said sleeve extending into an opening in said spacer, said opening being slightly larger than said sleeve, and a wedge on the wall of the sleeve and embedded in the edge of the opening to press the sleeve against one side of the hole and prevent lateral movement of the sleeve in the hole.

3. A thin walled tubular cathode sleeve, an insulating spacer of thin friable material with a hole to receive one end of the sleeve, said hole being slightly larger than said sleeve, and a longitudinally extending relatively sharp-edged ridge, with a tapered end, on one side of said sleeve terminating short of the end of the sleeve, said end of the sleeve being inserted through said hole to embed said ridge in the edge of said hole to wedge the sleeve against one side of the hole.

NORVAL H. GREEN. 

